Screw-propeller.



D. W. TAYLOR.

SCREW PROPELLER. APPLIOATION FILED NOV. 11, 1907.

4 SHEETS-SHEET 1.

Patented Oct. 13, 1908.

D. W. TAYLOR. SCREW PROPELLER. APPLIOATION FILED NOV. 11, 1907.

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Patented Oct. 13, 1908.

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511mm I 1. c l 1 z 0 LI Ll D. W. TAYLOR.

SCREW PROPELLER.

APPLIOATION FILED NOV. 11,1907.

900,797. Patented Oct. 13,1908.

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DAVID W. TAYLOR, OF WASHINGTON, DISTRICT OF COLUMBIA.

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specificafionot Letters Patent.

Patented Oct. 13, 1908.

Application filed November 11, 1907. Serial No. 401,666.

tains to make and use the same, reference being had to the accompanyingdrawings, and to letters or figures of reference marked thereon, whichform a part of this specification. a

My invention relates to the method and means for preventing cavitationat propeller blades, and comprises essentially, the ex-' hausting of airfrom behind the blade at that part of the blade where cavitation occurs.

Referring to the drawings, in which like parts are similarlydesignated-Figure 1 is the customary developed cylindrical sectionthrough the ogival-shaped blade, the shaded portion showingapproximately the area of cavitation. Fig. 2 is a section through apropeller shaft and hub on line 2-2 of Fig. 3, showing the developedoutline of the blade in relation thereto, with the developed centralcylindrical section as is customary, and showing my invention appliedthereto. Fig. 3 is a section taken on the line 33 of Fig. 2. Fig. 4 is aview similar to' Fig. 2, showing a modifiedform of my invention. Fig. 5is a section .on the line 5-5 of Fig. 4. Fig, 6 is a view similar toFig. 4 showing a modification of the automatic pumppassage.

In the operation of a propeller, as its speed and thrust increases, apoint is reached at which the phenomenon knownas cavitation appears. Atlow s'peeds and thrusts the propeller is surrounded, front and rear, bypractically solid water. The driving face thrusts the water astern andthe rear face sucks it astern. But, though thereis prob ably more orless eddying and disturbed motion in the water adjacent to the rearface,

' that is to say, the point at which the'suction of the back of theblade is so great that the water is unable .to follow the blade andbreaks away from it, thus producinga cavity behind the blade somewhat asindicated by the shaded area Fig. 1. If this cavity were a vacuum,cavitation would not be nearly so objectionable. It would mean simplythat the suction of the back of the blade would reach a maximum equal tothe atmospheric pressure plus the water pressure due to the submergenceof the blade. As a matter of fact, however, cavitation sets in atthrusts far below those which would be shown with ,vacua behind theblades, and the cavities occurring are not vacua, but filled with watervapor, whose pressure is of no importance in ractical cases, and withair which is drawn gem the water. The air is the cause of the trouble.Owing to its pressure in the cavity, there is little or no suction fromthe back of the blade, water is not drawn into the propeller disk, andpractically the whole thrust is obtained from the face of the blade withexcessive slip and low efficiency.

There have been at least two methods used to avoid cavitation with moreor less success. The most common is the use of excessively broad bladeswith great surface. These, owing to their breadth, offer less suction atthe back fora given slip and speed, owing to their finer entrance andmore gradual acceleration and retardation of the water moving past them.Also for a given thrust and speed, the slip is less than fora -blade ofordinary width. The excessively broad blades, however, ofl'er excessivefrictional resistance, and thus waste much power.

The second general method of avoiding cavitation is by the use of bladeswith sections specially shaped, so that the acceleration and retardationof the water are more gentle than with the ordinary types of sections,and hence the blades can be worked to higher thrusts before cavitationsets in,

than blades of the usual ogival section, while i are in communicationwith the cavities when ls, recesses or passages which open orcavitationsetsup. Through these channels or passages I pump or otherwise exhaustthe air as fast as it enters the cavities thus maintaining any desireddegree of vacuum at the backs of the blades.

Referring more particularly to Figs. 2 and 3, the propeller shaft 5 isprovided with the usual tapered end 6 on which the propeller hub 7 issecuredsin any of the usual and well known manners. Now in order toprovidemeans for exhausting the air from the back of the blades, Iformat the root of each blade in the hub, a recess 8 which communicatesby means of a passage 9 preferably but not necessarily, radial to theshaft with a central bore 10 in the shaft, which central bore 10communicates with any suitable exhausting appliance and to this end maybe connected with the ships condenser and thus with the main air pump orto a special pump or a jet of steam may be used for exhaustmg the air orany other well known method or apparatus for causing suction may beused." OED the-back. of each blade 11 and preferably but notnecessarily, on the following half of the blade, I form a. cavity orrecess 12 that may communicate directly or indirectly with one of therecesses 8 and in this particular construction I have shown the recess12 communicating with a shorter recess 13 which in turn communicatesthrough the root of the blade by a passage 14 with the chamber 8. Ihavethus showntwo connected recesses but it is obvious that I may varythe shape and outline thereof and to form a single recess as therequirements of construction of a particular shape of blade may permit.The larger recess 12 is covered by a plate 15 provided with perforations16 and a plate 18 may or may not be perforated. The plates arecountersunk in the blade 11, are-held in lace by screws 19 or any othersuitable f stening devices and are shaped to give a fair contour to theback of the blade. The blade is rotated in the direction of the arrowshown at the top; of the figure and during the rotation the cavitation,which is greater at the following side of the blade, is reducedby drawinthe air from the cavity behind the blade t rough the perforations 16into the recess 15 in the blade 6, then through 13,

the passage, 14, recess 8 and hole 9 to the central bore 10 in the shaftto the exhausting device. In-practice when the propeller is at rest thepassages will fill with water and it will be desirable to provide avalve in the vicinity of the pumpv or other exhausting device for thepurpose of shutting out the water. I have mentioned in connection withthese two figures, special means for exhausting 5 the air produced bycavitation from behind the back of the blade towards its center andthrough its shaft, but Figs. 4 and 5, illustrate a modification in whlchI show recesses some? in the form of slots 20 connected togetherpreferably at one of their ends, here shown as near the root of theblade at 21 and provided with a perforated countersunk cover plate 22screwed or otherwise secured in place.

In place of radial channels 20 I may use a single cavity in the body ofthe blade. Adjacent the cavity or cavities 20, I provide a pump passage23 passing substantially from end to end of the blade covered by an imerforate plate 24. This assage is prefera ly straight and radial and 15open at both the root and the tip of the blade, the entrance being shownat 25 and the exit at the tip of the blade at 26. The chamber or'- theconnected chambers or recesses 20 communicate with these passages 23 bymeans of one or more short passages 27 preferably inclined toward thetip .of the blade.

In orderto provide suflicient thickness at the tipof the blade foraccommodating the cover plate 23, it becomes sometimes necessary toslightly increase the thickness of the blade at this point as shown bythe shading at 28 in Fig. 4, however, this is not always necessary.

The operation of this structure is as follows: When the blade is inrapid rotation water will enter the pump passage 23 at 25 near the rootof the blade and by reason of the centrifugal force set up will causethe water to be thrown from the channel 24 at the tip of the blade 26 bycentrifugal force. The water thus moving through the channel 24' bycentrifugal force draws or entrains with it the air through 27 and therecess or chambers 20 which in turn communicate through theirperforations 16 with the cavity in the water behind the blade andthereby exhaust the air from said cavity by the centrifugal force set upby the movement of the propeller itself. Such a construction isautomatic in its action and does not require special exhausting devices.

In certain cases 1t will be necessary to construct the channel or pumppassage 23 as shown in Fig. 6, where this passage is shown asconstricted or reduced at a point between the inlet 25' and the outlet26 and at the point 30 where the assage 27 enters the pump passage 23.Sue a structure will reduce the pressure in 22, or in other wordsincrease the suction of air.

I claim:

1. The method of preventingcavitation at screw propellers whichcomprises exhaustically and centrifugally discharging the air,

from the blades by their rotation 6. The method of, preventingcavitation at' screw propellers which comprises admitting the air fromthe cavity formed at the back of the blades into the body of the bladesand exhausting it therefrom by an entraining current of watermoved bycentrifugal force through the blade.

7. A propeller blade having a recess formed therein, a perforated coverfor said recess and means for exhausting the recess, whereby the cavityformed in the water at the blade may be exhausted.

8. A propeller blade having a recess formed therein, a perforated coverfor said recess, and a pump passage communicating with the recesswhereby the recess may be exhausted.

9. A propeller blade having a recess therein, a perforated cover for therecess presented to' the water and means to automatically exhaust saidrecess by the movement of the propeller.

10. A-propeller blade having a recess on the back thereof, a perforatedplate cover- 'ing said recess, a pumping passage leading portion.

substantially through the blade and ports connecting the pumpingpassage'and-recess.

11. A propeller blade having a recess in v the following half of theback thereof, a per- I forated cover plate for said recess a pumppassage leading from the root to t e tip of the blade and, portsinclined toward the tip of the blade 7 connecting said passage andrecess.

of connected recesses in the following half of the back of the blade, aperforated cover for said recesses, a pump passage passing radiallythrough the blade and ports directed toward the tip of the blade andconnect ing the recesses to the passage near the root of the blade.

13. A propeller blade having a recess formed therein communicating withthe cavity formed in the water at the back of the blade and meanscarried by the blade for exhausting said recess and cavity.

14. A propeller blade having formed therein communicating wlth thecavity formed in the water at the back of the blade and means forautomatically exhausting said recesa .15. A propeller blade having arecess formed therein communicating with the cavity formed in the waterat the backof the a .recess blade and a pump passage through the bladerestrictedQintermediate its ends and com municating with the recess atthe restricted In testimony that I claim the foregoing as my invention,I have signed my name in presence of two subscribing witnesses.

. DAVID w. TAYLORQ Witnesses B. W. SOMMERS, HENRY ORTH, Jr.

. 50 12. -A propeller blade having a plurality

